Assessing contamination of microalgal astaxanthin producer Haematococcus cultures with high-resolution melting curve analysis

The Clinical Promise of Microalgae in Rheumatoid Arthritis: From Natural Compounds to Recombinant Therapeutics

Rheumatoid arthritis (RA) is an invalidating chronic autoimmune disorder characterized by joint inflammation and progressive bone damage. Dietary intervention is an important component in the treatment of RA to mitigate oxidative stress, a major pathogenic driver of the disease. Alongside traditional sources of antioxidants, microalgae-a diverse group of photosynthetic prokaryotes and eukaryotes-are emerging as anti-inflammatory and immunomodulatory food supplements. Several species accumulate therapeutic metabolites-mainly lipids and pigments-which interfere in the pro-inflammatory pathways involved in RA and other chronic inflammatory conditions. The advancement of the clinical uses of microalgae requires the continuous exploration of phytoplankton biodiversity and chemodiversity, followed by the domestication of wild strains into reliable producers of said metabolites. In addition, the tractability of microalgal genomes offers unprecedented possibilities to establish photosynthetic microbes as light-driven biofactories of heterologous immunotherapeutics. Here, we review the evidence-based anti-inflammatory mechanisms of microalgal metabolites and provide a detailed coverage of the genetic engineering strategies to enhance the yields of endogenous compounds and to develop innovative bioproducts.

Biotechnologies for bulk production of microalgal biomass: from mass cultivation to dried biomass acquisition

Microalgal biomass represents a sustainable bioresource for various applications, such as food, nutraceuticals, pharmaceuticals, feed, and other bio-based products. For decades, its mass production has attracted widespread attention and interest. The process of microalgal biomass production involves several techniques, mainly cultivation, harvesting, drying, and pollution control. These techniques are often designed and optimized to meet optimal growth conditions for microalgae and to produce high-quality biomass at acceptable cost. Importantly, mass production techniques are important for producing a commercial product in sufficient amounts. However, it should not be overlooked that microalgal biotechnology still faces challenges, in particular the high cost of production, the lack of knowledge about biological contaminants and the challenge of loss of active ingredients during biomass production. These issues involve the research and development of low-cost, standardized, industrial-scale production equipment and the optimization of production processes, as well as the urgent need to increase the research on biological contaminants and microalgal active ingredients. This review systematically examines the global development of microalgal biotechnology for biomass production, with emphasis on the techniques of cultivation, harvesting, drying and control of biological contaminants, and discusses the challenges and strategies to further improve quality and reduce costs. Moreover, the current status of biomass production of some biotechnologically important species has been summarized, and the importance of improving microalgae-related standards for their commercial applications is noted.

A green decontamination technology through selective biomineralization of algicidal microorganisms for enhanced astaxanthin production from Haematococcus pluvialis at commercial scale

Currently, there is a lack of an efficient, environmentally-benign and sustainable industrial decontamination strategy to steadily achieve improved astaxanthin production from Haematococcus pluvialis under large-scale outdoor conditions. Here, this study demonstrates for the first time that a CaCO₃ biomineralization-based decontamination strategy (CBDS) is highly efficient in selectively eliminating algicidal microorganisms, such as bacteria and fungi, during large-scale H. pluvialis cultivation under autotrophic and mixotrophic conditions, thereby augmenting the astaxanthin productivity. Under outdoor AT and MT conditions, the average astaxanthin productivity of H. pluvialis using CBDS in a closed photobioreactor system was substantially increased by 14.85- (1.19 mg L^-1 d^-1) and 13.65-fold (2.43 mg L^-1 d^-1), respectively, compared to the contaminated H. pluvialis cultures. Given the exponentially increasing demand of astaxanthin, a natural anti-viral, anti-inflammatory, and antioxidant drug, CBDS will be a technology of interest in H. pluvialis-based commercial astaxanthin production which has been hindered by the serious biological contaminations.

Comparison of various approaches to detect algal culture contamination: a case study of Chlorella sp. contamination in a Phaeodactylum tricornutum culture

Microalgal contamination in algal culture is a serious problem hampering the cultivation process, which can result in considerable economic and time losses. With the field of microalgal biotechnology on the rise, development of new tools for monitoring the cultures is of high importance. Here we present a case study of the detection of fast-growing green algae Chlorella vulgaris (as contaminant) in a diatom Phaeodactylum tricornutum culture using various approaches. We prepared mixed cultures of C. vulgaris and P. tricornutum in different cell-to-cell ratios in the range from 1:10³ to 1:10⁷. We compared the sensitivity among microscopy, cultivation-based technique, PCR, and qPCR. The detection of C. vulgaris contamination using light microscopy failed in samples containing cell ratios <1:10⁵. Our results confirmed PCR/qPCR to provide the most reliable and sensitive results, with detection sensitivity close to 75 cells/mL. The method was similarly sensitive in a pure C. vulgaris culture as well as in a mixed culture containing 10⁷-times more P. tricornutum cells. A next-generation sequencing analysis revealed a positive discrimination of C. vulgaris during DNA extraction. The method of cultivation media exchange from sea water to fresh water, preferred by the Chlorella contaminant, demonstrated a presence of the contaminant with a sensitivity comparable to PCR approaches, albeit with a much longer detection time. The results suggest that a qPCR/PCR-based approach is the best choice for an early warning in the commercial culturing of microalgae. This method can be conveniently complemented with the substitution-cultivation method to test the proliferating potential of the contaminant. KEY POINTS: • PCR-based protocol developed for detection of Chlorella cells. • Synergy of various approaches shows deeper insight into a presence of contaminants. • Positive/negative discrimination occurs during DNA extraction in mixed cultures. • Newly developed assays ready to use as in diagnostics of contamination.

A review of high value-added molecules production by microalgae in light of the classification

This work reviews applications of high added value molecules produced from microalgae. Older forms of valorization - health food and quality feed, polyunsaturated fatty acids, pigments, carbohydrates - are currently penetrating their markets. They are driven by desirable properties: texturer and dye for food industry, antioxidant for cosmetics and the appetite of the general public for biosourced compounds. Most recent developments, such as peptides, vitamins, polyphenols, phytosterols and phytohormones, are struggling to meet their market and reach economical competitiveness. Still they are pushed forward by the very powerful driver that is pharmaceutical industry. In addition this work also proposes to link microalgae phyla and related potential applications. This is done through highlighting of which bioactive compounds can be found in which phyla. While some seem to be restricted to aquaculture, Cyanobacteria, Chlorophyta and Rhodophyta show great promises.

Effect of Ca(OH)2 dosing on thermophilic composting of anaerobic sludge to improve the NH3 recovery

The primary biological treatment method for organic sludge is composting and/or anaerobic digestion, but their product (compost or biogas) is of little economic benefit; therefore, an improved process to produce a high-value product is required to make sludge management more sustainable. Maximizing NH₃ gas recovery during composting processes has the potential benefit of producing high-value microalgal biomass. However, the majority of produced ammonia does not evaporate as NH₃ gas but retains as NH₄⁺-N in the compost after fermentation. The present study investigates the effects of the timing of Ca(OH)₂ dosing (on days 2, 5, and 9), and the Ca(OH)₂ dose (1.1-2.6 mmol/batch), on lab-scale thermophilic composting of anaerobic sludge. The effects on NH₃ recovery, organic matter degradability, and microbial activity are evaluated. Ca(OH)₂ dosing immediately improved the emission of NH₃, with yields 50-69% higher than those under control conditions. The timing of the dosing did not influence NH₃ recovery or organic matter degradability. Higher Ca(OH)₂ doses resulted in higher NH₃ recovery, while microbial activity was temporarily and marginally inhibited. The pH of the compost reached 10-11.5 but quickly dropped to 8-8.5 within a day, probably because of neutralization of Ca(OH)₂ by the emitted CO₂ and release of NH₃, which maintained the microbial activity. The present study indicated that Ca(OH)₂ dosing would be useful to apply during thermophilic composting for NH₃ recovery to cultivate high-value microalgal biomass, which enables this process to obtain a more economic benefit.

A novel, nature-based alternative for photobioreactor decontaminations

Large-scale microalgae cultivations are increasingly used for the production of animal feed, nutritional supplements and various high-value bioproducts. Due to the process size and other limitations, contaminations of microalgae fermentations with other photoautotrophic microorganism are frequently observed. In the present study, we explored the applicability of 5-isobutyl-2,3-dimethylpyrazine for the removal of contaminating microalgae from industrial photobioreactors. In order to select a representative microbial population for susceptibility experiments, reactor samples were obtained from a multi-stage cultivation process. Assignments of 18S rRNA gene fragment amplicons indicated that Haematococcus, Chlorella, and Scenedesmus were the three most frequently occurring microalgae genera in the selected reactors. Following the isolation of representative algae cultures, susceptibility tests were conducted with the antimicrobial pyrazine. It was demonstrated that all isolated contaminants are highly susceptible to the bioactive compound. The highest tolerance towards the alkylpyrazine was observed with Scenedesmus vacuolatus; solutions with 1.66% (v/v) of the active compound were required for its deactivation. Further tests with the vaporized pyrazine showed consistent reductions in the viability of treated microalgae. This pilot study provides evidence for the applicability of a novel, nature-based alternative for bioreactor decontaminations.

A new approach for detection and quantification of microalgae in industrial-scale microalgal cultures

In industrial-scale microalgal cultures, non-target microalgae compete with the desired species for nutrients and CO₂, thus reducing the growth rate of the target species and the quality of the produced biomass. Microalgae identification is generally considered a complicated issue; although, in the last few years, new molecular methods have helped to rectify this problem. Among the different techniques available, DNA barcoding has proven very useful in providing rapid, accurate, and automatable species identification; in this work, it is used to assess the genomic identity of the microalga species Scenedesmus sp. 'almeriensis', a common strain in industrial-scale cultures. Barcode markers rbcL and ITS1-5.8S-ITS2 were sequenced and the obtained genomic information was used to design a quantitative PCR assay to precisely quantify the S. almeriensis concentration in microalgal cultures of industrial interest. TaqMan chemistry was used to quantify down to 1 μg/L dry weight of S. almeriensis cells, including in the presence of concentrated mixed cultures of other microalgae. A simple direct qPCR approach was also investigated to avoid classic DNA extraction and to reduce total assay time to approximately 2 h. The objective was to design strain-specific tools able to confirm and quantify the presence of different strains in whatever microalgae culture so as to achieve maximal productivity and quality of the produced biomass.